With the continuous development in integrated circuit technology, electronic products are increasingly developing in a direction of miniaturization, intellectualization, high-performance and high-reliability. Integrated circuit (IC) package not only has direct influence on the performance of integrated circuit, electronic module and even the whole machine, but also restricts the miniaturization of the whole electronic system, the low-cost and reliability.
Under these circumstances, electronic industry has made higher and higher requirements on IC package technology. Therefore, integrated circuit fabrication is miniaturized, which causes a rise in logic circuits contained in the chips, and increases the number of chip input/output (I/O) pin. To meet the demands, many different methods for package come into being, such as Ball Grid Array (BGA), Chip Scale Package (CSP), Multi Chip Module package (MCM package), Flip Chip Package, Tape Carrier Package (TCP), Wafer Level Package (WLP), etc.
Nowadays, the BGA package technology is becoming very popular in advanced integrated circuit package. The BGA package technology is a surface mount package that utilizes an array of ball bumps on the back of the substrate to replace traditional leads, which provides semiconductor devices with high level integration and excellent performance. The BGA package technology significantly increases the number of I/O pins of semiconductor devices and reduces the pitch between the pads, which makes the packaged devices have smaller size and save the space occupied by the packaged devices, and thus makes the miniaturization of semiconductor devices with high density, high performance and multi-pin such as PC chipset and microprocessor become possible.
Bump formation technology is a key technology in BGA. Usually the breakdown of BGA is caused by the failure of bumps, so the reliability of the bumps is the main factor to be solved in the development of BGA package technology. In the prior art, solder deposits on a piece of chip metal bedding through some certain technological processes. Bumps are the metal solder balls formed after reflowing under certain temperature.
With the increasing integration of semiconductor devices, distances between bumps decrease rapidly. Bumps at the edge are liable to peel off because the edges of the chip are far from the central point, and in conditions of periodic variation of temperature, the stress on the bumps at the edge is greater than that closer to the central point. In order to maintain the mechanical intensity of a bump, volume of the bump needs to be enlarged. However, due to the mutual soluble physical property of metals, increasing volume of all bumps in limited area will make the bumps become larger and turn to a lateral move. This may cause bridging between bumps, then lead to further short-circuit, and finally influence the electrical property of semiconductor devices.